PROJECT SUMMARY/ABSTRACT Impaired driving continues to be a major public health concern with over 10,000 deaths caused by alcohol- related vehicle crashes every year. A growing concern is polysubstance impaired driving, specifically when drivers are impaired by both alcohol and marijuana. Rates of simultaneous alcohol and marijuana use (SAM) and vehicle crashes are high among young adults, indicating a need for research on predictors of driving while SAM impaired (D-SAM) and riding with a driver who is SAM impaired (R-SAM) to inform prevention intervention efforts for this population. The current study proposes two phases of research to assess risk and protective factors of D-SAM and R-SAM. Phase 1 will utilize the statewide Washington Young Adult Health Survey sample of more than 7,000 young adults to collect norms on SAM, D-SAM and R-SAM and assess their association with risky driving-related outcomes. Phase 2 will collect a new sample of young adults (N=400) and utilize measurement burst design to examine how norms and motives to use alcohol, marijuana, and SAM are associated with D-SAM and R-SAM at the global and event level. Global assessments will be at baseline and 6 months. Participants will also complete once a day event-level surveys on Thursdays, Fridays, Saturdays and Sundays every other week for 6 months. The association of demographics, personality characteristics, and mental health factors on event-level D-SAM and R-SAM will also be assessed, as these factors have previously been shown to be associated with risky and impaired driving behaviors. This research is innovative in that while there is empirical support for norms and motives as predictors of alcohol and marijuana use and consequences, limited research has examined them in the context of SAM use or impaired driving behaviors, and no research has examined how they predict D-SAM or R-SAM. Further, there has been almost no research that has assessed event-level predictors of any type of impaired drivers. The findings from the current study may be used to inform prevention and intervention efforts and the entities that implement them. The proposal includes strong collaborations with state level entities, specifically the Washington College Coalition for Substance Abuse Prevention, Washington Traffic Safety Committee and the Division for Behavioral Health and Recovery. Through partners we will 1) help identify a list of key stakeholders on preventing impaired driving, specifically D-SAM and R-SAM in WA, 2) provide information on their current projects, barriers, and supports for prevention of D-SAM and R-SAM, 3) deliver feedback on the current study's measures and assessments, and 4) facilitate dissemination and translation though several avenues at the local and state levels. Thus, the current project has the potential to impact D-SAM and R-SAM prevention efforts and reduce unnecessary fatalities and injuries caused by these impaired driving-related behaviors.